1. Field of the Invention
The present invention relates to a waveguide structure that is particularly suitable for transmission of high frequency signals in a microwave band and a millimeter wave band, an antenna apparatus that uses that waveguide structure, and a vehicle radar apparatus in which a waveguide structure or an antenna apparatus is used.
2. Description of the Related Art
Conventional waveguide structures have: a metal first conductive member in which a first groove that has an opening on a flat surface is formed; and a metal second conductive member that is formed so as to have a flat plate shape, that is disposed on the surface of the first conductive member so as to cover the first groove of the first conductive member, and that is fastened to the first conductive member by screws, a waveguide being configured between the first groove of the first conductive member and the second conductive member.
However, when flat first and second conductive members are fastened using screws, the fastening forces from the screws do not act uniformly on the surfaces of the facing first and second conductive members. Thus, buckling may occur in the thin plate-shaped second conductive member, giving rise to gaps between the first and second conductive members that communicate between internal and external portions of the waveguide. In such cases, high frequency signals may leak out through the gaps between the first and second conductive members when propagating through the waveguide, giving rise to problems such as deterioration in energy transmission efficiency of the high frequency signals, etc.
When a plurality of waveguides are configured on the above waveguide structure, because it is necessary to fasten walls that partition off a plurality of first grooves that are formed on the first conductive member and the second conductive member using screws, the waveguides cannot be placed closer to each other than a diameter of the screws, giving rise to problems such as being unable to reduce the waveguide structure in size, etc. In other words, it may not be possible to adapt the above waveguide structures to waveguide structures for the transmission of high frequency signals in the microwave band and the millimeter wave band for which reductions in size are being demanded. Other problems also arise such as deterioration in isolation between the waveguides, etc.
As structures that suppress deterioration in isolation between the waveguides, or deterioration in energy transmission efficiency when the high frequency signals propagate through the waveguides, etc., that results from gaps that communicate between internal and external portions of the waveguides, there have been proposed:
conventional high frequency signal transmission casings in which waveguides are configured by joining together first and second conductive members by means of a conductive rubber material (see Patent Literature 1, for example);
first conventional waveguide slot array antennas in which waveguides are configured by joining together first and second conductive members by means of a conductive pressure sensitive adhesive sheet (see Patent Literature 2, for example); and
second conventional waveguide slot array antennas that fix first and second conductive members using an adhesive to configure waveguides, and that have bumps that are made of a conductive resin that are disposed in advance so as to penetrate that adhesive to ensure continuity between the first and second conductive members (see Patent Literature 3, for example).
In addition, there have been proposed:
conventional waveguide pipes in which waveguides are configured by joining together first and second conductive members by frictional stirring and bonding (see Patent Literature 4, for example); and
conventional waveguide converters that suppress leakage of high frequency signals from gaps that communicate between internal and external portions of waveguides between first and second conductive members, if such gaps arise, by forming a second groove that has a predetermined depth that has an opening on a surface of the first conductive member in close proximity to both sides of a first groove in a width direction (see Patent Literature 5, for example).    [Patent Literature 1]: Japanese Patent Laid-Open No. HEI 8-186401 (Gazette)    [Patent Literature 2]: Japanese Patent Laid-Open No. 2003-318641 (Gazette)    [Patent Literature 3]: Japanese Patent No. 3650083 (Gazette)    [Patent Literature 4]: Japanese Patent No. 3610274 (Gazette)    [Patent Literature 5]: Japanese Patent No. 3843946 (Gazette)
In conventional high frequency signal transmission casings, two waveguides are configured in a casing that has an opening on one surface by integrating a conductive rubber material between a bottom surface of a partitioning plate and the casing, fixing the partitioning plate and the conductive rubber material using screws, and fixing a conductive cover to an opening edge portion of the casing so as to cover two first grooves that are constituted by the partitioning plate and the casing. Here, because the conductive rubber material is elastically deformed by being pressed and held between the casing and the partitioning plate, it is placed in close contact with the partitioning plate and the casing, enabling gaps near the bottom of the first groove to be eliminated.
In conventional high frequency signal transmission casings, the conductive rubber material is interposed between the bottom surface of the partitioning plate and the casing, but eliminating gaps between the internal portion and the external portion of the waveguides of the waveguide structure by applying the conductive rubber material so as to be interposed between the first and second conductive members of the above waveguide structure is easily conceivable.
However, even if a conductive rubber material is interposed between the above first and second conductive members, when a plurality of waveguides are to be configured, it is necessary to fix the walls of the first conductive member that partition off the first grooves and the second conductive member using screws, and problems remain such as being unable to reduce the waveguide structure in size. In addition, because electroconductivity of the conductive rubber material is small compared to metal, energy transmission loss is increased when high frequency signals propagate through waveguides in a waveguide structure to which the conductive rubber material has been applied compared to when the waveguides are configured using only metal.
Because volume of the conductive rubber material reduces as it deteriorates with the passage of time, gaps may arise that communicate between internal and external portions of the waveguides as time passes. It is also commonly known that the rate of temperature change in the electroconductivity of a conductive rubber material is high. In other words, another problem has been that optimal waveguide conditions for efficiently propagating high frequency signals cannot be maintained against the passage of time and temperature changes in a waveguide structure to which conductive rubber has been applied.
First conventional waveguide slot array antennas have a construction in which a conductive slot plate and base body that constitute a waveguide are joined together using a conductive pressure sensitive adhesive sheet. Because the slot plate and the base body are thereby placed in close contact with the conductive pressure sensitive adhesive sheet, gaps that communicate between internal and external portions of the waveguide can also be eliminated.
However, conductive pressure sensitive adhesive sheets have characteristics are such that not only is their electroconductivity small compared to the electroconductivity of metal, their rate of temperature change is high, and their volume reduces as they deteriorate with the passage of time. Consequently, although reductions in size are enabled because first conventional waveguide slot array antennas perform joining together of the slot plate and the base body by adhesion of the conductive pressure sensitive adhesive sheet without using screws, with regard to other points they have similar problems to waveguide structures to which the conductive rubber material has been applied.
Second conventional waveguide slot array antennas have a construction in which a slot plate and a base body that are made of metal that constitute waveguides are joined together by an adhesive, and bumps that are constituted by a conductive resin that are disposed in advance on adhesive positions of the slot plate pass through the adhesive to contact and communicate with the base body. Gaps that communicate between internal and external portions of the waveguide can thereby also be eliminated.
Because second conventional waveguide slot array antennas perform joining together of the slot plate and the base body using an adhesive without using screws, reductions in size are enabled. If a predetermined adhesive is selected, the degree of degradation of the adhesive as time passes can also be reduced compared to the conductive rubber material and the conductive sheet.
However, because continuity between the slot plate and the base body is performed only by the bumps, one problem has been that electrical continuity between the slot plate and the base body is insufficient, increasing energy transmission loss when high frequency signals propagate through the waveguides.
Because conductive members of conventional waveguide pipes are joined together by frictional stirring and bonding, the conductive members are joined together without gaps, enabling increases in energy transmission loss when high frequency signals propagate through the wave guides to be suppressed. However, joining together of the conductive members by frictional stirring and bonding is performed beyond the joined portion between the conductive members. Consequently, problems remain such as conventional waveguide pipes not being able to respond to demands for reductions in size.
In conventional waveguide converters, because space for the second grooves that are formed on two sides in the width direction of the first groove must be ensured on the first conductive member, problems remain such as not being able to respond to demands for reductions in size. Even if the conventional waveguide converters could hypothetically be reduced in size by forming the second grooves on the first conductive member accurately with an extremely small width, new problems arise such as increased costs related to forming the second grooves.